ARS | Publication request: MEASURING SURFACE ROUGHNESS HEIGHT TO PARAMETERIZE RADAR BACKSCATTER MODELS FOR RETRIEVAL OF SURFACE SOIL MOISTURE 1704

Submitted to: IEEE Transactions on Geoscience and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 14, 2006
Publication Date: January 15, 2007
Citation: Bryant, R., Moran, M.S., Thoma, D., Holifield Collins, C.D., Skirvin, S.M., Rahman, M., Slocum, K., Starks, P.J., Bosch, D.D., Gonzalez-Dugo, M.P. 2007. Measuring surface roughness height to parameterize radar backscatter models for retrieval of surface soil moisture. IEEE Geosci. and Rem. Sens. Letters 4(1): 137-141.

Interpretive Summary: There is much interest in creating soil moisture maps for climate change studies, agricultural production, and overland vehicle mobility. Radar images from satellites are being used for this purpose. Radar images are sensitive to soil moisture and the roughness of the ground (surface roughness). Computer programs have been written to analyze these images in order to extract soil moisture information but for them to work, the surface roughness in the image must be known. Surface roughness is difficult to measure on the ground yet needs to be measured very precisely for these computer programs to accurately predict soil moisture. This study investigates different techniques to measure surface roughness and gives some recommendations for procedures to make accurate roughness measurements. These improved roughness measurements can further the goal of making real time, precise soil moisture maps that can used as a tool for understanding our environment and making more efficient use of our water resources.

Technical Abstract: Surface roughness is a very important input for radar backscattering models that are used to predict soil moisture. The most common measurement of roughness is rms height (hRMS). We analyze ground based roughness measurements at four locations taken with two instruments, a pin meter and a laser scanner. We also measure a smooth floor to compare instrument characteristics. Issues addressed include, the number of measurements needed to obtain a representative sample of a site, instrument noise when measuring a smooth surface, and the effects of detrending on different lengths measurement trasnsects. Results show that the hRMS for a smooth floor are 0.15 cm and 0.35 cm for the pinmeter and laser scanner respectively. To get a representative sample of roughness at a site, at least 20 1-meter length measurements should be made. At transect lengths greater than 1-meter, transects should be detrended at 1 meter segments to get a consistent measurement of roughness.